1. Field of the Invention
The present invention relates to a toner for developing an electrostatic latent image applied to a developer used to develop an electrostatic latent image in electrophotography, electrostatic recording, electrostatic printing and the like, to an image forming method and an image forming apparatus using the toner.
2. Description of the Related Art
As to full-color images produced by an electrophotographic method, there has recently been an increasing demand for the development of high quality and highly precise full-color images. Full-color images produced by an electrophotographic method are not on a level satisfying general customers familiar with printed images. To satisfy this demand, studies are being made for bringing the level of such full-color images close to that of prints or photographs.
Also, along with recent ecological trends, not only toxicity tests typified by the AMES test and skin sensitivity tests for toners have been made, but studies concerning limitation of the addition of dioxin-generating materials such as halogens to toners have also been made. Moreover, as to dyes and pigments which are colorants contained in a toner, when strong light such as a xenon flash is used to carry out fixing, most dyes are sublimated and, in most pigments, a part of byproducts are sublimated and deteriorated by light. Thus, there are cases where the intended color reproducibility is not obtained.
For the above reason, it is urgently necessary to develop toners which (1) have a wide color range, (2) have high ecological properties, (3) have good light fastness, (4) do not allow colorants to be sublimated by intense light (high temperature) and (5) are relatively inexpensive.
Therefore, as colorants used for toners, those having high tinting strength, excellent color vividness and high light fastness, as well as high dispersibility in a resin, are strongly desired.
Although many pigments for magenta toners have been proposed so far, quinacridone type pigments are widely used due to the fact that they have excellent color vividness and transparency and are also superior in light fastness.
For example, a toner singly containing 2,9-dimethylquinacridone is disclosed (see, for example, Japanese Patent Application Laid-Open (JP-A) Nos. 49-27228, 57-54954 and 1-142559). However, this toner is not regarded as a sufficiently vivid magenta toner though it has high light fastness.
Also, attempts are made to blend Rhodamine dyes with various pigments (see, for example, JP-A Nos. 5-34980, 5-11504 and 4-268571). However, these toners cannot be used because the Rhodamine dye is sublimated when flash fusing is carried out. Although the Rhodamine dye is not sublimated when these toners are used for heat roll fixing, these toners have the problem that the Rhodamine dye is discolored within a few days when the toner is stored outdoors because the Rhodamine dye has low light fastness.
It has been proposed to use quinacridone type pigments (C.I. Pigment 122) and a carmine (C.I. Pigment Red 57:1) or to blend a naphthol type pigment (C.I. Pigment Red 184 or C.I. Pigment Red 238) with a C.I. Pigment Red 57:1 to improve color developing ability (see, for example, JP-A Nos. 9-179348 and 2003-162097). Although these proposals achieve a balance between cost and color reproducibility, the C.I. Pigment Red 57:1 pigment is decomposed when flash fusing is carried out, leading to deteriorated color tone and blackish prints. Also, when this toner is used for heat roll fixing, it has the problem that color blurring occurs when the toner is stored outdoors for a long period of time because the light fastness of the C.I. Pigment Red 57:1 is somewhat weak.
Moreover, a colorant has been proposed which is produced using 2,9-dimethylquinacridone and an unsubstituted quinacridone having the following structure as a magenta colorant, has the intended hue and is intended to improve the frictional electrification characteristics of a toner (see, for example, JP-A Nos. 62-291669 and 10-97102). Since an unsubstituted quinacridone is used in this case, it has strong light fastness and is resistant to deterioration in both the case of flash fusing and the case of heat roll fixing. However, it has been found that since quinacridones having different chemical structures are blended, the dispersibility of a pigment is impaired and color reducibility is slightly deteriorated in the case of general-purpose mixing without carrying out a so-called master batch process. Also, it is a matter of concern that 2,9-dimethylquinacridone is expensive.
This magenta toner may be used in the case of using a heat roll. However, it is known that, in contrast with a heat roll fixing system, a flash-fusing system enables ultra-high speed printing because contact with a medium is decreased in the flash-fusing system (see, for example, JP-A Nos. 2002-156775 and 2002-182422). Thus, there is a demand for a magenta toner in which the aforementioned problems have been solved and which is compatible not only with fixing using a heat roll, but with a fixing apparatus utilizing the above-described flash-fusing system.